Hexavalent chromium has emerged as a contaminant of significant concern in environmental waters. For example, one source of this contaminant has been the use of hexavalent chromium, in the form of sodium dichromate, to prevent corrosion in the cooling water systems of nuclear reactors. Spills and leaks of sodium dichromate concentrates, and direct discharge of hexavalent chromium-bearing cooling water to the ground surface have released hexavalent chromium to the environment. Some of that hexavalent chromium has reached groundwater aquifers.
For the purposes of environmental monitoring of hexavalent chromium in wells and water bodies, and for controlling engineered processes used to remediate contaminated water, frequent measurements of hexavalent chromium are required. Visible range colorimetry based on the Beer-Lambert law is the most commonly used analytical method used to perform the measurements. However, the visible range colorimetric method depends on treating samples with chemical reagents to react with the hexavalent chromium to produce a visible red-violet color whose intensity is related to the concentration of the hexavalent chromium in the sample.
While sensitive and accurate, the visible range colorimetric method has disadvantages. The samples often require filtration to eliminate turbidity, caused by suspended particulate matter, which interferes with colorimetric measurements. Because of the need for both filtration and chemical treatment, the method is not readily adaptable to continuous process monitoring or to in situ measurements in wells or water bodies. Further, the chemically-treated water samples, along with ancillary packaging materials, single-use reagent ampoules, and the like, constitute waste that in itself requires careful and appropriate handling and disposal.
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